Research goals in this project: To determine the effects of smoking low and high nicotine cigarettes on pulmonary circulation on man, to estimate lobar pulmonary capillary blood flow, diffusing capacity, oxygen consumption, and pulmonary capillary and tissue volume in unanesthetized sheep, to estimate pulmonary hemodynamics in exercising sheep and finally, to improve the estimation of pulmonary capillary plus tissue volume by using multiple soluble gases in addition to acetylene during the rebreathing procedure. BIBLIOGRAPHIC REFERENCES: Begin, R., Epstein, M., Sackner, M.A., Levinson, R., Dougherty, R., and Duncan, D.: Effects of water immersion to the neck on pulmonary circulation and tissue volume in man. J. Appl. Physiol. 40: 293-299, 1976. Levinson, R., Epstein, M., Sackner, M.A., Begin, R.: Comparison of the effects of water immersion and saline infusion on central hemodynamics in man. Clin. Sci. & Molec. Med., 1977.